Vehicular exhaust gas treatment systems are used to treat the exhaust gas from an engine of the vehicle. The exhaust gas emitted from a diesel engine, is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOX”) as well as condensed phase materials (liquids and solids) that constitute particulate matter. Catalyst compounds, typically disposed on catalyst supports or substrates that are disposed within the exhaust gas treatment system, are provided to convert certain or all of these exhaust gas constituents into non-regulated exhaust gas components. For example, diesel exhaust gas treatment systems may include one or more of a precious metal containing diesel oxidation catalyst (“DOC”) converter for the reduction of CO and excess HC, a selective catalytic reduction (“SCR”) device for the reduction of NOX with the assistance of a diesel exhaust fluid (“DEF”), and a diesel particulate filter (“DPF”) device for the removal of particulate matter.
The SCR operation for the reduction of NOX described above generates dinitrogen oxide (N2O). It is preferable to design the exhaust gas treatment system in such a way as to minimize N2O output from the SCR device.